The present invention relates to sheet registration devices and, more particularly, to such devices and to similar arrangements as found in the context of printing or copying machines.
For an appreciation of xerographic apparatuses and processes, particularly with respect to sheet feeding and registration devices associated therewith, reference may be had to the following U.S. Pat. Nos. 3,339,917; 3,902,715; 3,957,366 and 4,023,792.
It is an important requirement in the functioning of xerographic and similar copying machines that the copy paper to which the xerographic image is to be transferred be precisely and carefully registered with such image as formed on a photoconductive matrix, whereby the desired end of having the copy reproduce the original exactly may be effectuated. For this purpose, a copy paper gate or gating device is effective to control the registration process. Thus, a sheet of copy paper is normally fed out of a feeder tray and up to the paper gate. The paper gate controls the insertion of a projection into the path of a given copy sheet, so as to stop that sheet. Then when the projection is removed, the sheet will advance in timed relationship to the rest of the machine according to the logic system employed. The operation is continuous such that the aforesaid projection is successively reinserted into the same path to stop the next sheet.
Just before the photoconductive matrix reaches a transfer roller or similar device, the copy sheet being advanced is carried beyond the paper gate device and is subsequently fed between the powder image on the conductive matrix and the transfer roller. As a result, the image is transferred onto the copy paper and is registered as precisely as possible. For example, the point on the copy paper at which an image begins or ends is within one-sixteenth of an inch from the corresponding point on the matrix image. However, attainment of this precise registration is affected by the speed of the reproduction process. Consequently, when it is desired, for example, to produce copies in relatively short periods such that the speed of the copy paper moving within the machine is of the order of ten inches per second, the time period or "window" that is allotted to the registration process is extremely limited. Accordingly, the time allowed for the paper gate solenoid to perform its functions so that the projection or "finger" will be able to react and to reset is severely restricted.
As a result of the aforenoted restrictions, it has been found that a vexing problem arises in the effort to produce exact registration, particularly when fourteen inch copy paper is involved in the process. What has occurred is that the trailing edge of the paper is clipped such that velocity change then takes place, resulting in undesirable effects.
It will, of course, be appreciated that it is impractical, if not impossible, to build all of the components in a copy machine to a virtually perfect degree of accuracy. Instead, conventional tolerances are accepted and some sort of adjustable means is provided for the purpose of exactly synchronizing the copy paper movement with the movement of the photoconductive matrix. In a conventional machine to be described, the adjustment mechanism includes a gap which is provided between the feed roller for the copy paper and a spring clamp member which engages a shaft of such feed roller. When the paper gate assembly is actuated, the feed roller is brought into pinching engagement with a continuously driven roller, thereby to advance a given copy sheet. Normally what is done is that this gap, which is precisely located between a plastic button provided on the spring clamp and the feed roller shaft, is adjusted to have a value from 0.020 inches to 0.040 inches (0.030 inches nominal).
However useful the slight adjustment of the aforenoted gap is in accomplishing the required synchronization, it turns out that substantial adjustment of this gap for the purpose of curing the vexing problem of trail edge clipping of fourteen inch paper is ineffective. This is because any tampering with the tolerances set on this gap inevitably results in improper pressure being applied to different copy papers that may be utilized in the machine. For example, different weights and grades of paper are commonly utilized and if this gap is not kept within the strict tolerance limits that have been specified, proper pressure will not be afforded for driving each kind of copy paper, with all that that means in terms of misregistration of the copy paper with the photoconductive matrix.
Accordingly, it is the primary object of the present invention to solve the aforenoted problem of trail edge clipping of fourteen inch copy paper as experienced in a xerographic copying process.
Another object is to compensate and correct for the variations in mechanical settings and in the different reluctance properties of paper gate solenoids, which factors tend to create varying time lags, from machine to machine, between electrical activation and the actual mechanical movement of the paper gate solenoid.
Another object of the invention is to provide for electronic adjustment in the delay that is provided in the resetting of a paper gate device.